docs: def check_restructuredtext(self):
          """
          Checks if the long string fields are reST-compliant.
          """
          # Warn that this command is deprecated
          # Don't use self.warn() because it will cause the check to fail.
          Command.warn(
              self,
              "This command has been deprecated. Use `twine check` instead: "
              "https://packaging.python.org/guides/making-a-pypi-friendly-readme"
              "#validating-restructuredtext-markup"
          )
  
          data = self.distribution.get_long_description()
          content_type = getattr(
              self.distribution.metadata, 'long_description_content_type', None)
  
          if content_type:
              content_type, _ = cgi.parse_header(content_type)
              if content_type != 'text/x-rst':
                  self.warn(
                      "Not checking long description content type '%s', this "
                      "command only checks 'text/x-rst'." % content_type)
                  return
  
          # None or empty string should both trigger this branch.
          if not data or data == 'UNKNOWN':
              self.warn(
                  "The project's long_description is either missing or empty.")
              return
  
          stream = _WarningStream()
          markup = render(data, stream=stream)
  
          if markup is None:
              self.warn(
                  "The project's long_description has invalid markup which will "
                  "not be rendered on PyPI. The following syntax errors were "
                  "detected:\n%s" % stream)
              return
  
          self.announce(
              "The project's long description is valid RST.",
              level=distutils.log.INFO)